Oil chage question

Hi guys, well my oil change was due and dealer was so bz that he told me to wait another month so i took it to a near by place they always deal with mercedes i have 1993 400e with original 45,500 miles and dealer always puts in full synthtic 5-40 valvorine this time i mentiones these people that but when i went to pick it up i asked them about the job they told me that they my mistake put 10-20 in it and they refused to change it for me for no additional cost they charged me 85.00 same as the dealer i brought my own oil filter so alltogether it just costed me 95 bucks (i know its crazy) now my question is this wether i can leave it inside or get another oil change ASAP how big of a difference in those two kinds car is smooth but its too heavy now its not runing i mean picking up as fast as before
thanks in advance
mani